Pile clamp for power hammers



United States Patent Inventors Hugo H. Cordes PILE CLAMP FOR POWER HAMMERS [56] References Cited UNITED STATES PATENTS 1,310,408 1/1919 Boardman 173/92 FOREIGN PATENTS 123,998 1931 Austria 173/92 Primary Examiner-James A. Leppink Attorney-Melville, StrassenFoster and Hoffman ABSTRACT: A clamping device for a power hammer of the type having a housing and ramreciprocable by fluid pressure, the clamping device comprising at least one cylinder having transverse clamping means solidly contacting the pile to be driven, the cylinder being supplied with pressure fluid from the ram, thereby controlling clamping pressure between the hammer housing and pile along with fluid pressure for the downward stroke of the ram. A return spring may be provided for retraction of the clamping piston.

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9 .4. ATTOR NEYS 1 FILE CLAMP FOR POWER I'IAMMERS BACKGROUND OF THE INVENTION Power hammers for driving piles, sections, pipes and the like, whose ram impacts upon the object being driven not only by free fall, but also under the effect of additional downward force exerted by fluid pressure, are designed with a heavy hammer housing in order to prevent the upward reaction force from lifting the hammer housing during the downstroke. As a result, such power hammers must have considerable weight and require lifting equipment of considerable load-bearing capacity.

The purpose of the present invention is to reduce the total weight of the hammer unit by the dead weight which acts merely to balance the reacting force, and thus to permit using lifting equipment of smaller load-bearing capacity, which in turn will reduce the capital investment involved.

It has previously been proposed to solidly tie together the hammer housing and the pile by a mechanical pile clamp and a spring arrangement. The pile then is useful because of its loading effect, but the driving action is reduced by the tensioning of the spring during the acceleration of the pile. It has also been suggested to permanently connect the hammer housing to the pile by a slidable pile clamp actuated by the pressure medium. Upon impact the hammer housing will become strongly accelerated, which will markedly reduce the driving effect and introduce severe stresses into the housing. In the event that the driving action causes slippage between the pile and the jaws of the clamp, the hammer housing and pile will drift apart.

Furthermore, it isknown that the hammer housing may be I temporarily clamped'to an impact plate which is slidably connected to the hammer and has the shape ofa hollow core to be inserted into a tubular pile. While such a clamping joint can reduce the weight of the hammer housing it cannot reduce that of the entire hammer unit, the impact plate being integral with the hammer unit.

SUMMARY According to this invention, these drawbacks are avoided by the provision of a clamping device adjoined to the hammer housing and consisting of at least one clamping cylinder and clamping means acting transversely'to the driving direction, which effects a solid interconnection with the objectbeing driven, whereby a longitudinal displacement between the hammer housing and the object being driven is virtually inhibited temporarily, and means for feeding the clamping cylinders with pressure fluid from the cylinder space causing the downwardly motion of the ram, because the clamping pressure between hammer housing and driven object iscontrolled together with the fluid pressure for the downward motion of the ram.

In this manner, the hammer is tied intimately to the object to be driven during the downward motion of the ram up to the instant immediately-preceding the impact upon the said object. Advantage is taken of the mass of the said object, so that the power hammer unit can be constructed with less weight and less expensively. When the object is a pile, the friction of the pile shell in the ground adds its effect to the mass of the pile. That influence is especially marked with piles that are hard to drive, and the hammer can then work to best advantage. Because of the temporary clamping, the pile is stretched between blows, which reduces the shell friction in the ground. Extra long piles will show better penetration because of the sequence of elongations and compressions.

I, By another embodiment of the inventive principle, the jclamping piston can be retracted by a spring, and a damping 'piston can be provided inside the clamping cylinder or the supply line, which will not interfere with the supply of the actuating fluid but will delay the retreat of the clamping piston after a partial releasing stroke.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawings show, by way of example, preferred embodiments of the invention.

FIG. I is a longitudinal section of the power hammer with the clamping device having a housing resting upon the pile via an impact plate;

FIG. 2 is the lower portion of the power hammer with the clamping device, with the housing resting immediately upon the head ofthe pile;

FIG. 3 is the power hammer equipped with an impact plate and clamping device for driving tubular piles;

FIG. 4 is an enlarged longitudinal section through the clamping cylinder with a damping piston provided inside the clamping piston; and

FIG. 5 is a longitudinal section through another modification of the clamping cylinder, with a damping piston located in the supply line.

DESCRIPTION OF THE PREFERRED EMBODIMENTS cylinder may be chosen. A clamping cylinder 10 is connected to the upper cylinder space 8 via line 9; the cylinder may be equipped with one clamping piston 11, or with two pistons 11 and l1,and it is attached to the hammer housing 1.

Hammer housing 1 rests upon a pile 12, either immediately, as in FIG. 2, or with the interposition of an impact plate 13, as in FIG. 1, or ofa pad 14, as in FIG. 3, for internal clamping in the case oftubular pileslS.

With the automaticcontrol valve 7 acting as shown in the drawing (FIG. I), the upper cylinder space 8 is connected to the return line 16, and hence depressurized. Ram 2 is raised, and clamping piston 11 is released. After reversal of control spool 7 the upper cylinder space 8 is connected to the supply line, and ram 2 is accelerated downward because of the excess pressure of the greater piston area.

Simultaneously, housing I tends to move up because of the reaction involved, which is counteracted because piston 11 supplied with the line pressure holds pile 12 against jaw 17, and retains it by friction. Shortly prior to the impact, control valve 7 is reversed automatically, which releases the clamping pressure; pile 12 or 15 is then driven in without entraining the hammer housing.

To ensure prompt clamping and releasing action of the clamping piston with minimum fluid motion, it is preferred that a return spring 18 be installed in clamping cylinder 10 which pulls back clamping piston 11 as soon as clamping cylinder 10 becomes depressurized. After a free partial upstroke has occurred, further retracting is damped as a result of axial movement of piston 11 relative to a damping piston 20 thus closing apertures 19 in damping piston 20; throttle bore 23 remains the only exit (see FIG. 4).

For piles of different sizes, the design in FIG. 5 will be more suitable. Here, the damping piston 21 is inside cylinder 10, or in supplyline 9; regardless of the position of clamping piston 11 it willallow a certain amount of fluid to escape freely at each unloading before its conical front edge will obturate the port toward line 9, with throttle bore 22 remaining thereafter as the only exit point.

Because of the throttling action of bores 22 and 23, clamping piston 11 will gradually move back to its ultimate point of return, so that the power hammer can be removed from the pile even when the pile head has been flattened out.

. We claim:

1. A power hammer comprising a hammer housing, a ram movable up and down within the said housing by fluid pressure, and a clampingdevice supported by the hammer housing, said clamping device comprising a clamping cylinder and clamping means arranged transversely to the driving direction of said ram to provide solid clamping engagement with the object to be driven so that relative longitudinal motion between the said hammer housing and the object to be driven can be temporarily inhibited, and the said clamping cylinder arranged to be supplied with pressurized fluid from a cylinder space which effects the downward acceleration of said ram so that the clamping pressure between the said hammer housing and the object to be driven is controlled in accordance with the fluid pressure causing downward motion ofthe said ram.

2. The structure claimed in claim I. wherein said clamping means includes at least one clumping piston, and a spring arranged to retract said clamping piston when said clamping cylinder is depressurized. v t

3. The structure claimed in claim 2, including a damping piston in said clamping cylinder movable axially with respect to said clamping piston'and so arranged that the supply of pressure to said clamping cylinder remains unobstructed while the return of said clamping piston following afree releasing stroke is delayed.

4. The structure claimed in claim 2, including a damping piston in said clamping 'cylinderor in said supply means so arranged that the supply of pressure fluid to said clamping cylinder remains unobstructedwhile the return of said clamping piston following a free releasing stroke is delayed.

5. A power hammer comprising a hammer housing, a ram movable up and down within the said housing by fluid pressure, and a damping device supported by the hammer housing to effect a solid contact between the object to be driven and the hammer housing by' means of fluid pressure. whereby said clamping device comprises in part a clamping cylinder and means for supplying said clamping cylinder with a pressure 

